SAR images refocusing on specific grids for ... · 3 4th TanDEM-X Science Team Meeting, 12-14 June...

1 4th TanDEM-X Science Team Meeting, 10-14 June 2013, German Aerospace Center (DLR)

Andrei ANGHEL1, Gabriel VASILE2, Guy d’URSO3, Remy BOUDON3, Didier BOLDO3, Jean Philippe OVARLEZ4, Irena HAJNSEK5

1 GIPSA-lab / University Politehnica of Bucharest2GIPSA-lab, French National Council for Scientific Research (CNRS)

3Électricité de France (EDF)4ONERA

5German Aerospace Center (DLR)

SAR images refocusing on specific grids for interferometric processing


On Off

SAR Image Grid

-Grid Reflectors.

Off-grid reflectors:• Loss of contrast.• Ambiguous phase.• False target detections.


SAR Image Defocusing

Focused SAR Image

Flight Path

Defocusing RAW data

0.5 1 1.5 2 2.5

x 104

0.5

1

1.5

2

2.5

x 104


SAR Image Refocusing

Refocused SAR Image ona specific grid.

Flight Path

Refocusing

RAW data

New grid

0.5 1 1.5 2 2.5

x 104

0.5

1

1.5

2

2.5

x 104

x [m]

y [m

]

Refocused SAR Image [dB]

-100 -50 0 50 100

-100

-50

0

50

100 -40

-35

-30

-25

-20

-15

-10

-5

0


X-band Ground-based SAR Imaging System1

Range [m]C

ross

-Ran

ge [m

]

SAR Image

0.5 1 1.5 2 2.5 3-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

-25

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0

1Andrei Anghel, Gabriel Vasile, Remus Cacoveanu, Cornel Ioana, Silviu Ciochina, “Short-Range Wideband FMCW radar for millimetricdisplacements measurement”, submitted to IEEE Transactions on Geoscience and Remote Sensing.


Ground-based SAR Images Refocusing (1)

Range [m]

Cro

ss-R

ange

[m]

SAR Image

0.5 1 1.5 2 2.5 3-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

-25

-20

-15

-10

-5

0

Defocusing Refocusing on a different grid

x [m]

y [m

]

Refocused SAR Image

0.5 1 1.5 2 2.5-0.5

0

0.5

1

-25

-20

-15

-10

-5

0

Computing the response fromeach pixel on the syntheticaperture elements.

Applying the back-projectionalgorithm on the de-chirpedraw data (the defocusedimage).


x [m]

y [m

]

Refocused SAR Image

0.5 1 1.5 2 2.5-0.5

0

0.5

1

-25

-20

-15

-10

-5

0

Ground-based SAR Images Refocusing (2)

Range [m]

Cro

ss-R

ange

[m]

SAR Image

0.5 1 1.5 2 2.5 3-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

-25

-20

-15

-10

-5

0

Defocusing Partial Refocusing on a different grid

Selecting only a certain targetfrom the initial image (using abinary mask).

Applying the back-projectionalgorithm on the de-chirpedraw data (the defocusedimage).


Ground-based SAR Refocused Images Interferogram

Range [m]

Cro

ss-R

ange

[m]

Coherence

1 1.5 2 2.5 3 3.5

-1

-0.5

0

0.5

1 0

0.2

0.4

0.6

0.8

1

Range [m]

Cro

ss-R

ange

[m]

Interferogram (rad)

1 1.5 2 2.5 3 3.5

-1

-0.5

0

0.5

1 -3

-2

-1

0

1

2

3

1 2 3 4 50

1

2

3

4

LOS

Dis

plac

emen

t (m

m)

n

realmeasured

1 2 3 4 50

0.02

0.04

0.06

0.08

Abs

olut

e er

ror (

mm

)

n


Spotlight High-Resolution TerraSAR-X images (300 MHz)


Focused TerraSAR-X spotlight image

RAW Data Corrections:-Taylor approximation in ECS.-Element pattern of antenna array.-Curved orbit compensation.-Stop-and-Go Approximation.-Tropospheric effects.

Spotlight RAW Data

Extended Chirp Scaling Algorithm 2

Focused Image

Corrected RAW data

For staring spotlight 1

1Pau Prats-Iraola, Rolf Scheiber, Marc Rodrıguez-Cassola, Steffen Wollstadt, Josef Mittermayer, Benjamin Brautigam, Marco Schwerdt, Andreas Reigber and Alberto Moreira, “High Precision SAR Focusing of TerraSAR-X Experimental Staring Spotlight Data”, in Proc. IGARSS’12, Munich, Germany, pp. 3576-3579.

2Alberto Moreira, Josef Mittermayer and Rolf Scheiber, “Extended Chirp Scaling Algorithm for Air- and Spaceborne SAR Data Processing in Stripmapand ScanSAR”, IEEE Transactions on Geoscience and Remote Sensing, Vol. 34, No. 5, Sept. 1996, pp. 1123-1136.


Refocusing TerraSAR-X images

SAR Image

Reversed Extended Chrip Scaling

Algorithm

De-chirping

RAW data

De-chirped RAW data

Back-projection algorithm

Grid Points

Reading Parameters from XML file: Central Frequency Chirp Bandwidth RSF PRFs Scene Coordinates ...

Refocused SAR Image

Extended CSA: FFTs/IFFTs Complex multiplications


Refocusing TerraSAR-X images : First Results (1)

Range [m]

Azi

mut

h [m

]

-2000 -1000 0 1000 2000

-2000

-1000

0

1000

2000

Flight PathR0 θ

Refocused Area

New Grid


Range [m]

Azi

mut

h [m

]

-1600 -1500 -1400 -1300 -1200 -1100 -1000

-1500

-1400

-1300

-1200

-1100

-1000

-900

-800

-700

-600

x [m]

y [m

]


-500 0 500

-500

-400

-300

-200

-100

0

100

200

300

400

500

Refocusing TerraSAR-X images : First Results (2)

Initial Image [dB]

40 dB dynamic range


Lon [deg]

Lat [

deg]


3.71 3.7105 3.711 3.7115 3.71244.4395

44.44

44.4405

44.441

44.4415

-40

-35

-30

-25

-20

-15

-10

-5

0

Flight Path

Further Research (1)

• The resolution issues in the refocusing process.• Refocus the raw data in latitude-longitude geometry using a GPS-measured grid.• Employ interferometric processing on refocused images.


Further research (2): Puylaurent dam displacementsmeasurement with TanDEM-X

GPS-measured points on the dam’s ridge.

Refocusing TanDEM-X images on the measured points.

Dam’s ridge displacements monitoring.


Thanks for your attention !!!

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SAR images refocusing on specific grids for ... · 3 4th TanDEM-X Science Team Meeting, 12-14 June...

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